Service most belt or chain CVTs with one full synthetic fluid

The increasing demands for further environmental compliance by automobiles in recent years have caused manufacturers to turn their attention to the continuously variable transmission (CVT) as a transmission technology that simultaneously achieves both performance and fuel economy.

CVT transmissions pose lubrication challenges that are different – and sometimes even tougher – than those of the planetary automatics that we are so familiar with. It’s a tricky balancing act. You need high metal friction so the belt grips well on the pulleys, but this and good anti-shudder durability tend to be opposite requirements – what works for one is detrimental to the other, so a balance needs to be found. The problem stems from the fact that the CVT chain or belt shares the same casing – and thus transmission fluid – as the torque converter or launch clutch; what is the optimum fluid for one may not suit the other. Thus, chemists have developed new formulations that allow the right balance to be struck. The deliberately slippery ingredients that encourage smooth, shudder-free engagement of the CVT’s clutches would normally make it impossible for the belt to grip; yet at the interface between belt and pulley, special compounds make the combination stick rather than slide. “Phosphorous, calcium and detergent-type chemistries have an affinity for getting onto that metal surface, as they form a film and help raise the friction by making it grabbier – they prevent the slipperier friction modifier components from getting into that surface and making the metal friction too low.” Furthermore, CVT performance is characterized by quietness and smooth acceleration without shift shocks, while it achieves fuel economy superior to that of other automatic transmissions by using integrated control with the engine to maintain a rotational speed range with high combustion efficiency.